Water-jet cutting apparatuses are well known in the art and have long been used in industry for cutting sheet materials of various types. Illustrative apparatuses are disclosed in British Pat. No. 1287585 and the following U.S. Pat. Nos. 3,877,334, 3,978,748, 4,006,656, 4,092,889, 4,116,097, 4,137,804, 4,312,254 and 4,501,182. The apparatuses typically include support means for supporting the sheet material to be cut, nozzle means for directing the high-velocity fluid jet against the material upon the support means, drive means for producing controlled relative movement between the nozzle and the supported material along two orthogonal axes, and energy dissipating means for receiving the fluid jet and dissipating the energy thereof following its penetration through the material being cut. The apparatus may further include, particularly when the material being cut consists of flexible fabric or the like, means for compressing the material against the support so as to prevent undesirable "flutter" or similar movement of it during the cutting operation. It is also known to provide fluid-jet cutting apparatuses with devices for facilitating the introduction therein of the material to be cut.
In most of the known fluid-jet cutting apparatuses, and particularly those that must perform relatively intricate cutting operations with a high degree of precision, the nozzle means is mounted for controlled bi-directional movement along two orthogonal axes, and the sheet material to be cut remains stationary during the cutting operation. Since in an apparatus of this type the nozzle moves over a large part of the underlying support means, the containment of and dissipation of energy from the fluid jet, following its passage through the material being cut, presents something of a problem. One previously proposed solution is to provide substantially the entire area of the support means with jet receiving and energy-dissipating means: see, e.g., U.S. Pat. No. 4,312,254. Another previously proposed solution utilizes a slotted support means and an underlying fluid-jet receiver that are aligned with each other and with the overlying nozzle means and that are moveable in unison therewith along at least one of the two orthogonal axes of movement of the nozzle: see, e.g., U.S. Pat. Nos. 4,137,804, 4,092,889 and 3,978,748. A disadvantage of apparatuses of either of the foregoing "stationary work" types is that the cost of maintenance and periodic replacement of the fluid jet receiving and energy dissipating components thereof is relatively great in comparison to the cost of maintaining and replacing components that are smaller and stationary. The difference in expense becomes particularly significant in the case of fluid-jet cutting apparatuses that are adapted to cut glass or other hard material, and which usually have particulate grit such as garnet entrained within the cutting fluid, since in this instance the components require much more frequent maintenance and/or replacement.
A stationary and relatively small fluid-jet receiving and energy-dissipating means may be employed in a fluid-jet cutting apparatus wherein the nozzle undergoes movement along only one of the two orthogonal axes, and the sheet material to be cut is moved by underlying support means along the other of the axes. U.S. Pat. No. 4,501,182 discloses an apparatus of this type in which the support means consists of a single driven belt or apron that supports material to be cut and that has longitudinally spaced flights on opposite sides of a slotted bridge that underlies the fluid discharging nozzle and that overlies the fluid receiving and energy-dissipating components of the apparatus. A somewhat similar apparatus having two separate article-supporting belts or aprons on opposite sides of an intervening slot is disclosed in British Pat. No. 1287585 and is discussed in the prior art description of U.S. Pat. No. 4,092,889. The latter patent points out that apparatuses of the foregoing type have significant disadvantages. They customarily are unable to achieve a high degree of precision in their cutting operations due to the difficulty or impossibility of driving the two work supporting belts at precisely the same speed and through identical displacements. As is noted in the patent, when the material or article to be cut is rigid and is supported and moved by two separate belts, its speed may vary at different times during the cutting operation depending upon which belt provides the dominant support. An additional difficulty is presented when the article or material supported and moved by the belt is not only rigid, but also smooth-surfaced. In this situation slippage may occur between the belts and the supported article or work, as well as between the belts and their drive components, with ensuing impairment of the precision of the cutting operation.
The aforesaid "slippage" disadvantage may be at least partially overcome with some rigid materials by the provision in the apparatus of additional moveable rolls and/or belts that overlie the sheet material to be cut and that force it downwardly into firmer engagement with the underlying supporting belt. However, this approach cannot be safely employed when material to be cut is sheet glass or similar material which is not only smooth and hard, but which is also highly susceptible to breakage and/or to becoming scratched and therefore rendered unsuitable for many intended utilizations. The problem of scratching of the glass is aggravated by the fact that particulate garnet or similar grit frequently must be and is contained within the cutting fluid used in the cutting operation. During at least the initial stages of each cutting operation, some of the grit entrained within cutting fluid will be deposited outside of the cutting area upon the upper surface of the glass. If the deposited grit is forced downwardly against the glass surface by an overlying roller or belt, particularly one that may not be driven at precisely the same speed as the glass sheet, scratching or other marring of the glass can easily ensue.
With the foregoing in mind, the primary object of the present invention is the provision of a fluid-jet cutting apparatus that is particularly, but not necessarily exclusively, adapted for efficiently and precisely cutting sheets of glass or similar material without breaking or otherwise damaging the material.